1. Field of the Invention
This invention relates to a color-separating apparatus for a liquid crystal projector, and more particularly to a color-separating apparatus for a liquid crystal projector of single panel type that is capable of improving light efficiency and color revival property.
2. Description of the Related Art
Generally, a projector projects a minute picture implemented at an internal small-dimension display onto a large-dimension screen with the aid of a projective lens on an expanded scale, thereby displaying a large-scale picture. This projector can be classified into a front projection system in which a picture is projected onto the front side of the screen and a rear projection system in which a picture is projected onto the rear side of the screen. A typical rear projection system of these systems includes a projection television. In the projector, a cathode ray tube (CRT) or a liquid crystal display (LCD) is used as a display device for providing a small-scale image. Recently, there has been highlighted a liquid crystal projector employing the LCD device profitable for making a thin-thickness projector.
The liquid crystal projector generally include a LCD device for providing a picture, a projection lens system for projecting the implemented picture onto the screen on an expanded scale, a light source for providing the LCD device with a light, an illuminating system for controlling a light path between the light source and the LCD device, and a driving circuitry for processing a signal.
The liquid crystal projector trends toward a realization of high brightness resulting from a configuration of better efficient optical system and a modification of a lamp system, or trends toward a simplicity of carrying and installation resulting from an implementation of small-size and light-weight device in spite of a reduced brightness. Such a liquid crystal projector uses a single or three LCD devices for a color realization. Generally, three LCD devices are employed if a high brightness is intended, whereas a single LCD device is employed if an implementation of small size and lightweight device is intended. A liquid crystal projector of single panel type adopting a single LCD device takes advantage of any one of a strategy of using a color filter, a strategy of separating three primary colors and inputting them at a specific angle and a strategy of sequentially sending three primary colors to the LCD device, for color realization""s sake. A picture-projecting apparatus in which three primary colors are sequentially sent to the LCD device typically employs a color wheel as shown in FIG. 1.
Referring to FIG. 1, a conventional optical system of a liquid crystal projector employing the color wheel includes a light source 2 for generating a white light, a color wheel 4 for transmitting only a specific color light of the white light from the light source 2, a condensing lens 6 for condensing a light, a polarizing prism 8 for reflecting and transmitting an incident light depending on a polarization direction thereof, a LCD device 10 for reflecting a light in an image signal to implement a picture light loaded with picture information, and a projective lens 12 for projecting a picture light from the LCD device 10 on an expanded scale.
The color wheel 4 is rotated by means of a motor 14 to transmit only a specific color light of a white light emitted from the light source 2 in accordance with its position. To this end, the color wheel 4 is divided into first to fourth filters 4A, 4B, 4C and 4D as shown in FIG. 2. The first to fourth filters 4A, 4B, 4C and 4D are coated or colored such that they can have a different color transmission characteristic, thereby transmitting red(R), green(G), blue(B) and white(W) lights, respectively. Such a color wheel 4 is rotated to position the first to fourth color filters 4A, 4B, 4C and 4D on a light path on a time-sequence basis, thereby allowing the red(R), green(G), blue(B) and white(W) lights on a time-sequence basis.
The condensing lens 6 focuses the color lights emitted from the color wheel 4 onto the polarizing prism 8. The polarizing prism 8 reflects a line-polarized light having a specific direction, that is, a S wave inputted from the condensing lens 6 into the LCD device 10 and, at the same time, outputs a P wave from the LCD device 10 to the projective lens 12.
The LCD device 10 is a reflective-type device, which continuously realizes red, green and blue picture in response to color lights reflected from the polarizing prism 8 and being incident thereto. The color picture continued by the LCD device 10 passes through the polarizing prism 8 and then is projected on a screen (not shown) on an expanded scale via the projective lens 12. In this case, an observer recognizes a combined color picture in which specific color pictures projected onto the screen are averaged on a time basis.
However, if the color wheel 4 shown in FIG. 1 is used, then there is raised a problem in that total light efficiency of the system is reduced to approximately ⅓ because all lights other than color lights transmitting the first to fourth filters 4A, 4B, 4C and 4D are reflected.
In order to compensate for this problem, there has been suggested an optical system employing a Dichroic mirror for a color separation and a rotation prism for converting progress directions of the separated color lights as shown in FIG. 3.
Referring to FIG. 3, the optical system of the liquid crystal projector includes a fly eye lens 18 and a polarizing beam splitter (PBS) array 20 arranged between on a light path between a light source 16 for generating a light and a first Dichroic mirror 24 for separating the light, first to sixth Dichroic mirrors 24, 28, 32, 46, 48 and 54 for transmitting and reflecting a specific wavelength band of light, first to third rotating prism 34, 38 and 42 for changing a light path in accordance with a rotation angle, a polarizing prism 60, and a LCD device 62.
The fly eye lens 18 divides a white light emitted from the light source 16 for each cell unit to focus it onto a specific area of the PBS array 20. The PBS array 20 separates an incident light into line-polarized lights having any one light axis, that is, a P wave and a S wave, and allows the S wave to be outputted as it is while allowing the P wave to be converted into a S wave with the aid of a half wavelength (xc2xdxcex) plate (not shown) partially attached to the rear side of the PBS array 20 so as to output the S wave. The first condensing lens 22 prevents a spread of a light emitted from the PBS array 20 and being incident to the first Dichroic mirror 24. The first Dichroic mirror 24 reflects and transmits incident lights in accordance with a wavelength band to separate them.
For instance, the first Dichroic mirror 24 reflects a red light of the incident lights while transmitting a green light and blue light. The second Dichroic mirror 28 reflects a red light reflected from the first Dichroic mirror 24 and being incident thereto via a second condensing lens 26 into the first rotating prism 34. The third Dichroic mirror 32 reflects a green light of lights transmitting the first Dichroic mirror 24 and being incident thereto via a third condensing lens 30 for allowing it to be progressed toward the second rotating prism 36 while transmitting a blue light for allowing it to be progressed toward the third rotating prism 42.
Each of the first to third rotating prism 34, 38 and 42 differentiates a progress direction of the red, green and blue lights in accordance with its rotation angle as shown in FIG. 4A to FIG. 4C. In other words, each of the first to third rotating prism 34, 38 and 42 differentiates positions of the red, green and blue lights imaged on the LCD device 62 depending on its rotation angel as shown in FIG. 5A and FIG. 5B. The red light transmitting the first rotating prism 34 is incident to the sixth Dichroic mirror 54 via a fourth condensing lens 36, the fourth Dichroic mirror 46 and a fifth condensing lens 50. The green light transmitting the second rotating prism 38 is incident to the sixth Dichroic mirror via a sixth condensing lens 40, the fourth Dichroic mirror 46 and the fifth condensing lens 50. The blue light transmitting the third rotating prism 42 is incident to the sixth Dichroic mirror 54 via a seventh condensing lens 44, the fifth Dichroic mirror 48 and an eighth condensing lens 52. The sixth Dichroic mirror 54 reflects incident red and green lights while transmitting an incident blue light. Each of the red, green and blue lights is incident to the polarizing prism 60 via a ninth condensing lens 56 and a polarizer 58 and then is reflected by the polarized prism 60 to be incident to the LCD device 62. In this case, as rotation angles of the first to third polarizing prisms 34, 38 and 42 are different from each other, the red, green and blue lights are imaged at a different area of the reflective LCD device 62 as shown in FIG. 6. Positions of the red, green and blue lights 62A, 62B and 62C imaged on the LCD device 62 in accordance with a rotation angle of the first to third rotating prisms 34, 38 and 42 rotated at a fast speed become different as they are continuously progressed in a certain direction as shown in FIG. 6. The LCD device 62 expresses red, green and blue color signals in conformity to red, green and blue lights being incident thereto with having imaged positions changed at such a fast speed, and continuously changes the color signals at a speed identical to a flow of the lights imaged on the LCD device 62. Accordingly, red, green and blue color image signals are sequentially implemented at any one area of the LCD device 62, so that an observer recognizes a signal integrated on a time basis.
The liquid crystal projector of single panel type employing the rotating prisms has an enhanced light efficiency because a light loss according to the color realization does almost not exist, but raises a synchronization problem of the rotating prisms. Particularly, although rotation timing between the rotating prisms is consistent at an initial time, it causes a gradual difference due to a deviation between driving devices of the rotating prisms with a lapse of time after a configuration of the system. If synchronization between the rotating prisms goes amiss, then color realization ability on the screen is deteriorated. Furthermore, if a lot of rotating prisms are used, then a lot of optical elements are required and an accurate color control is required, to cause a high cost.
Accordingly, it is an object of the present invention to provide a color-separating apparatus for a liquid crystal projector of single panel type that is capable of improving light efficiency and color revival property.
In order to achieve these and other objects of the invention, a color wheel apparatus according to one aspect of the present invention includes a color filter in which red, green and blue colors are formed in a spiral shape; and a reflective plate opposed to the color filter to reflect an incident light reflected and emitted from the color filter into the color filter again.
In the color wheel apparatus, the color filter takes a spiral shape in which red, green and blue colors are entered toward the rotation center direction.
The color filter is provided on a circular plate, and the reflective plate is provided at the rear side of the circular plate.
The reflective plate has a relatively smaller size than the color filter.
A color-separating apparatus for a liquid crystal projector of single panel type according to another aspect of the present invention includes a color wheel including a color filter in which red, green and blue colors are formed in a spiral shape, and a reflective plate opposed to the color filter to reflect an incident light reflected and emitted from the color filter into the color filter again; a condensing lens for focusing a color light emitted from the color wheel; a polarizing prism for reflecting and transmitting an incident light inputted from the condensing lens in accordance with a polarized direction; a display device for reflecting the color light reflected from the polarizing prism and being incident thereto in accordance with an image signal to implement a picture light loaded with picture information; and a projective lens for projecting the picture light from the display device on an expanded scale.
In the color-separating apparatus, the color filter takes a spiral shape in which red, green and blue colors are entered toward the rotation center direction.
The color filter is provided on a circular plate, and the reflective plate is provided at the rear side of the circular plate.
The reflective plate has a relatively smaller size than the color filter.
A color-separating apparatus for a liquid crystal projector of single panel type according to still another aspect of the present invention includes a color wheel having alternating red, green and blue concentric circles; and a full-reflecting mirror, being fixed to an incidence surface of the color wheel, for reflecting an incident light reflected and emitted from the incidence surface of the color wheel toward the color wheel.
In the color-separating apparatus, the full-reflecting mirror is fixed to the incidence surface of the color wheel in parallel.
The color wheel has the red, green and blue concentric circles spaced at the same distance d (wherein d is a positive number meeting a relationship of d greater than 0).
A rotation axis of the color wheel makes a non-axial rotating motion at a position spaced at the same distance d from a center axis of the concentric circles.
The color-separating apparatus further includes a driving motor for making a non-axial rotation motion of the color wheel.
The color-separating apparatus further includes a condensing lens for focusing a color light emitted from the color wheel; a polarizing prism for reflecting and transmitting an incident light inputted from the condensing lens in accordance with a polarized direction; a display device for reflecting the color light reflected from the polarizing prism and being incident thereto in accordance with an image signal to implement a picture light loaded with picture information; and a projective lens for projecting the picture light from the display device on an expanded scale.
The color wheel includes five color areas consisting of red, green, blue, red and green color areas to image an illuminating light on three areas of the five color areas.